In cold regions, a refrigerator is sometimes cut off electric functions completely to be used as a cabinet or a pantry for food storage. Additionally, because of installation location or the like of a refrigerator, user in some cases may want to switch off the power supply without taking trouble to disconnect the plug from the outlet. A thermostat having a forced switch-off mechanism matches both of above needs. Such a thermostat is disclosed for instance in Japanese Utility Model Unexamined Publication No. S54-45980. Next, a conventional thermostat is described with reference to drawings.
FIG. 4 shows a sectional view of a conventional thermostat and FIG. 5 shows a plan view of a cam body of the conventional thermostat. Sensor 1 converts temperature changes in a control section into pressure changes. L-shaped operation member (operation member) 2 makes contact with sensor 1 and can turn around supporting axis 13. An end of spring 3 is hooked near an end of vertical member 2B of operation member 2 and the other end of spring 3 is fixed to screw 4 that is screwed in housing 12. An end of rod 5 is fixed to vertical member 2B of operation member 2 and the other end of rod 5 is fixed to contact plate 6. Contact plate 6 is provided with moving contact 7 on its free end and is fixed to a terminal in the other end. Moving contact 7 connects to or disconnects from stationary contact 8. Cam 10 has curved surface 14 on circular cam body 9 internally. Finger grip shaft 11 protrudes out of housing 12. In the configuration described above, curved surface 14 of cam 10 makes contact with the distal end of vertical member 2B of operation member 2, allowing operation member 2 to slide along curved surface 14.
Next, operations of the thermostat having aforesaid configuration are described. Upon an increase in temperature of the control section, sensor 1 extends to move operation member 2 pivotally counterclockwise around supporting axis 13. When temperature of the control section exceeds a set-temperature, operation member 2 presses rod 5 leftward in the drawing against an elastic force of spring 3 (corresponding to the set-temperature) set by screw 4. Rod 5 presses contact plate 6 to connect moving contact 7 to stationary contact 8, causing a circuit for power supply to be closed.
On the other hand, upon a decrease in temperature of the control section, sensor 1 contracts to move operation member 2 pivotally clockwise around supporting axis 13 with the elastic force of spring 3. Then the pressure on contact plate 6 affected by rod 5 decreases gradually to reverse contact plate 6 at a predetermined temperature, causing moving contact 7 to disconnect from stationary contact 8 thereby causing the circuit for power supply to be opened. Thus, the thermostat can keep the temperature of the control section in a predetermined range.
Next, an operation forcing to open contacts independently of the temperature of the control section is described. Cam body 9 is moved pivotally in the direction indicated by arrow B to make a contact of curved surface 14 with the distal end of vertical member 2B of operation member 2 causing vertical member 2B to slide along curved surface 14. Then curved surface 14 moves operation member 2 pivotally clockwise around supporting axis 13. This releases the pressure affected by rod 5 to contact plate 6 to disconnect moving contact 7 from stationary contact 8. Closed contacts can be thus forced to open.
In the conventional configuration, rotating finger grip shaft 11 can force the thermostat to be switched off. At the time, the distal end of operation member 2 is forced to slide along curved surface 14 of cam body 9. However, a frictional force between the distal end of operation member 2 and curved surface 14, a surface condition of curved surface 14 and the like would likely to increase torque forces to rotate finger grip shaft 11. Moreover, the distal end of operation member 2 is applied pressures in two directions: leftward and frontward in the drawing. As a result, supporting axis 13 of operation member 2 is applied pressures in the similar directions, causing a position of supporting axis 13 to deflect from the position before the forced switch-off operation. This has risks to change the elastic force magnitude of spring 3 causing the set temperature to change.